Renal physiology: Distal CT and Collecting Duct Flashcards
roles of the DCT and collecting duct
absorb water and ions
DCt is divided into early and later
role of the early DCT
reabsorb Na+, Cl- and Ca2+
early DCT
impermeable to water
macula densa cells
dependent on Na+/K+ATPase transporter on basolateral membrane
excretes Na+ into the ECF
K+ in
reduced intracellular sodium, gradient favours active transport of Na+ into the cells through channel
the conc grad of Na allows Na to enter from the lumen of the DCT by NCC symporter, allows Cl too
Cl- exit cell through Cl uniporter on basolaterla membrane to ECF
preventing accumulation in the cell
Ca2+ utilises Na grad from the pump
on the basolaterla membrane there is NCX antiporter so Ca to the ECF
Na into the cell
reduciton of the intracellular Ca makes gradient and Ca in from the lumen of the tubule to cell through ca uniporter, secondary active transport
macula densa cells
sensory epithelium n tubuloglomerular feedback
control of GFR
parathyroid hormone in early DCT
binds PTH to recpetor
causes more Ca channels inserted
increases Ca reabsorption
2 main cell types in the late DCT
principle cell
intercalated cells
principle cells
majority of the tubular cells
Na+/K+ ATPase on basolaterla membrane
Na in
establishes gradient for Na to enter through ENaC
Na is postive and extruded and forms electrical gradient
K+ accumulation in the cell
due to the pump
promotes secretion of K+ to lumen of tubule
through K+ uniporter
function of intercalated cells
assist in acid base control of h+ and HCO3-
types of intercalated cells
A
B
type A intercalated cells
hydrogen ATPase
H+/K+ ATPase
secrete H+ into lumen
whilst reabsorbing HCO3-
bicarbonate formed intracellulary by carbonic anhydrase acting on CO2 and H2O
H+ in lumen reacts with HPO42- or NH3 to rpevent ions re-entering as new compounds are charged
excreted as they can’t pass the membrane
late DCt, preventing Cl- and K+ accumulation
K+/Cl- symporter on the basolateral membrane allows leakage back to the ECF
type B intercalated celsl
H+ and HCO3- channels on opposite sides of the cell
net effect is secretion of HCO3-
reabsorption of H+
important in alkalosis response
how is the DCT different to PCT in response to acidosis
cells actively secrete H+ in response to acidosis in the DCT
collecting duct
water reabsorption through action of ADH and aquaporins
ADH produced by hypothalamus stored in posterior pituitary until released
acts on kidney tubules to increase number of aquaporin 2 channels in apical membrane of collecting duct tubular cells
ADH binds to V2 on tubule cells
activates adenylyl cyclase
increase cAMP
vesicles containing aquaporin 2 channels deposit contents into apical membrane of tubular cells
increasing channels increase cell permeability
ability to reabsorb more water from filtrate and create smaller volumes of more concentrated urine
what does the basolateral membrane of collecting duct always have
aquaporin channels 3 and 4
